[R-sig-Geo] Spatial Query (Selection) with Apply

[Robin Lovelace]

Hi Ariel,

Glad it helped.

Yes you could place your apply command into a lapply to get a list of
matrices.

Something like this should work:

dist_list <- lapply(tmp, function(coord) {

   apply(X = coord, MARGIN = 1, FUN = function(x) spDistsN1(coord, x,
longlat = T)

}

Robin



On Tue, Aug 28, 2018 at 9:13 PM, Ariel Fuentesdi <ariel.fuentesdi using usach.cl>
wrote:

> Thanks, Robin
>
> It worked perfectly, although I transformed the data from sf to
> SpatialDataFrame objects with:
>
> zones <- as(zones, "Spatial")
> nodes <- as(nodes, "Spatial")
>
> The next step I will follow is to create Distance Matrix like this:
>
> coord <- tmp2[[1]]@coords
> dist1 <- apply(X = coord, MARGIN = 1, FUN = function(x) spDistsN1(coord,
> x, longlat = T))
>
> obviously, the task is a distance matrix for every selection. ¿What would
> you recommend, the aggregate function as you talked before or something
> like a nested apply?
>
> Regards,
> Ariel
>
>
>
> 2018-08-27 19:32 GMT-03:00 Robin Lovelace <rob00x using gmail.com>:
>
>> Hi Ariel,
>>
>> It helps when asking for help with code to produce a reproducible
>> example. To understand your input data I've created nodes and zones based
>> on the spData data nz_height and nz_elev. Based on the assumption you want
>> to find all the nodes in each zone I think the direct answer to your
>> question is something like the following:
>>
>> tmp2 = lapply(s, function(x) {
>>   nodes[zones[x, ], ]
>> })
>>
>> The longer answer is that aggregate(), st_join() +
>> aggregate()/summarize() may provide quicker solutions, depending on what
>> you want to do with the points after grouping them by which zone they fall
>> in.
>> Note: I've used sf objects based on the explanation here
>> https://geocompr.robinlovelace.net/spatial-operations.html#spatial-vec
>> which may not work with sp data but the aggregate code should work roughly
>> the same:
>>
>> # install.packages("sf")
>> # install.packages("spData")
>> library(spData)
>> library(sf)
>> #> Linking to GEOS 3.6.2, GDAL 2.2.3, proj.4 4.9.3
>> zones = nz
>> nodes = nz_height
>> tmp = list()
>> s = 1:nrow(nz)
>>
>> for(i in s) {
>>   tmp[[i]] = nodes[nz[i, ], ]
>> }
>>
>> # understand what's going on with plots (not shown)
>> # plot(st_geometry(nz))
>> # plot(st_geometry(tmp[[i]]), add = TRUE, col = "red")
>> # plot(nz[i, ], col = "green", add = TRUE)
>>
>> tmp2 = lapply(s, function(x) {
>>   nz_height[nz[x, ], ]
>> })
>>
>> identical(tmp, tmp2)
>> #> [1] TRUE
>>
>> Created on 2018-08-27 by the [reprex package](http://reprex.tidyverse.org)
>> (v0.2.0).
>>
>> I've also pasted the reprex into the geocompr github tracker so the plots
>> can be seen and the code formatted: https://github.com/Robinlovela
>> ce/geocompr/issues/294
>>
>> Hope this helps,
>>
>> Robin
>>
>>
>> On Mon, Aug 27, 2018 at 9:53 PM, Ariel Fuentesdi <
>> ariel.fuentesdi using usach.cl> wrote:
>>
>>> Hi,
>>>
>>> I want to do multiple selections of a point shapefile based on polygons
>>> on
>>> other layers, I can do this in a for loop, but I desire to do this in a
>>> function of the apply family.
>>>
>>> I named the point shapefile "nodes" and the polygons shapefile "zones".
>>>
>>> This is what I did:
>>>
>>> tmp <- list()
>>> for (i in 1:nrow(zones using data)) {
>>>     tmp[[i]] <- nodes[subset(zones, ESTUDIO == i),]
>>>     tmp
>>>   }
>>>
>>> But I have no clue how to change it to the apply family, can you provide
>>> an example of this?
>>>
>>> Thanks in advance.
>>>
>>> Regards,
>>> Ariel Fuentes
>>>
>>>         [[alternative HTML version deleted]]
>>>
>>> _______________________________________________
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>>> R-sig-Geo using r-project.org
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>>>
>>
>>
>

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